1. Field of the Invention
The present invention relates to a porous carbonized film with fine continuous pores and to a process for its production, and more particularly it relates to a porous carbonized film useful for purposes that require heat resistance, flexibility and mechanical strength, such as inorganic material carriers, micro-filtration filters, bug filters, heat sinks, heat exchangers, thermal radiators, adsorption films, reinforcing materials and the like, and to a process for production of a porous carbonized film that comprises carbonizing a porous film made of a highly heat resistant resin.
2. Description of the Related Art
Techniques have been proposed in recent years for carbonizing polymer films for use as carbonized films. It has become common to employ cellulose, thermosetting resins, pitch tar and the like as the precursor materials.
Japanese Unexamined Patent Publication No. 10-99664 discloses a carbonized film suitable for gas separation, prepared by carbonizing various aromatic polymers, wherein a cardo polymer is employed as the separating film.
Recently carbonized films have come into common use as heating elements and heat sinks. For example, Japanese Unexamined Patent Publication No. 10-312778 discloses a high-efficiency thermal radiator in which a carbonized film having straight pores is used. Japanese Unexamined Patent Publication No. 9-148490 discloses a circuit board made of a carbon material with excellent heat radiating properties. Japanese Unexamined Patent Publication No. 10-158308 discloses a heat-resistant bug filter for gas-phase polymerization. Japanese Unexamined Patent Publication No. 10-5521 discloses a filter element made of polyimide fibers that exhibits satisfactory strength and durability. Further, Japanese Unexamined Patent Publication No. 10-46484 discloses a heat-resistant porous paper sheet.
The aforementioned carbonization process involving carbonization from a cardo polymer is appropriate for separation of gas components, but it gives a small pore diameter and is therefore not suitable for filters and radiating films.
On the other hand, bug filters made of heat-resistant fibers or nonwoven fabrics have a mesh size of about 10 xcexcm or greater even when especially fine, and they therefore present the risk of inclusion of fiber scrap as contaminants when gases pass therethrough. It is therefore not suitable for purposes requiring micro-filtration. In addition, most organic fibers have thermal restrictions, and therefore their uses are limited.
For these reasons, it has been desired to develop a carbonized film with high heat resistance and low contamination.
Furthermore, adsorption films that have appropriate activity or that carry active adsorbing agents require large adsorption areas.
One process for production of the aforementioned carbonized films has been a process of carbonization by heating an organic polymer at high temperature in an anaerobic atmosphere, but this has a disadvantage in that the carbonization rate is low for carbonization of most organic polymers.
In contrast, aromatic polyimides of aromatic polymers attain a high carbonization rate and readily retain their pre-carbonization form. By selection of the carbonization temperature it is also possible to produce carbonized films with various properties. It is thereby possible to provide amorphous carbonized films or porous graphite films.
However, carbonization of aromatic polyimide films has not allowed their use as filters or adsorption films.
It is an object of the present invention to provide a porous carbonized film with fine continuous pores, and a process for its production.
The invention provides a porous carbonized film with fine continuous pores, obtained by carbonization of a highly heat-resistant resin porous film in an anaerobic atmosphere.
The invention further provides a process for production of a porous carbonized film with fine continuous pores, that comprises heating a highly heat-resistant resin porous film at 800xc2x0 C. or higher in an anaerobic atmosphere for carbonization.
Throughout the present specification, xe2x80x9ccontinuous poresxe2x80x9d will refer to so-called open pores that extend from either desired surface to the other surface with the fine pores forming channels, and the fine pores are preferably non-linear and follow a tortuous course.